OHARP is not a bad gig, if you can do it. Probably not waiting in A-pool, since they need you there just in case, but maybe later on in the VT's. I did it between primary and advanced, and basically got me 3 weeks of free leave to go home. I worked a total of about 3 days, as the office I went to really just considered it a good deal for me and didn't really need anyone anyway. I filled about 1000 envelopes of fliers, stamped them, threw them in a box my buddy had at his house, brought them back to the recruiter office at the end, and called it a TAD. Funny thing is that about a week later, the box showed back up at my buddies house with all the envelopes. Apparently the clerk at the recruiting office forgot to open the thing and send the letters out individually, so it got mailed back to the address that was originally written on the box. So basically my entire time there was for naught.
Eh, it depends. I got sent to work for some HR type who had maybe an hour's worth of work for me a day, but insisted I stay there all day long. Needless to say after a couple weeks I went back to my ROTC unit. I only took the job in the first place because originally I was told I would go to Pcola within a month after graduation and I wanted the time to wrap up some stuff at home. I ended up waiting 5 months after graduation to report.
Bottom line, if your ROTC unit is awesome, stay there for stash jobs, unless you have some pressing reason to go somewhere else.